1. Field of the Invention
The present invention relates generally to cleaning of the flue gases emitted from industrial and electric utility of coal fired boilers. More particularly, it relates to a method for removing acidic vapors, sulfur dioxide and carbon dioxide by mechanical and condensation method.
2. Description of the Prior Art
In the U.S. approximately 50 million tons of sulfur dioxide emits every year into the atmosphere from coal fired electric utility power plants, and from other large coal consuming facilities. In the past attempts to recover the sulfur dioxide from the flue gases were motivated by the increasing environmental regulations, some foresaw a glut of sulfur produced from recovery, but scrubbing of flue gases with lime or lime stone, which produces calcium sulfite-sulfate waste has dominated the flue gas desulfurization (FGD) systems market. These systems were used and continued to be recommended because they have proven to be effective, and because the equipment and scrubbing materials are well known and available. Other ways to meet air pollution requirements are by switching to low sulfur containing fuels, conversion of high sulfur coal to gas or oil with removal of sulfur during the processing, and removal of sulfur dioxide in the boiler by fluidized bed combustion methods.
At the present, the wet scrubbing lime systems have dominated the FGD field, the addition of magnesium oxide or sodium based solution have been also used in flue gas scrubbing systems, there are many other chemical processes that have been used or developed to remove sulfur dioxide from the flue gases, identified as the throw away processes which creates disposal problems in connection with liquid or solid wastes, other chemical processes and methods have been proposed to treat the wasted materials and keep them from being environmentally hazardous. The high cost and energy needed for mining, manufacturing, handling, storing and disposing of the lime and limestone and their by-products in the wet scrubbing systems has appeared to be the stumbling block for the installation of the flue gas desulfurization systems.
It is well known that sulfur is one of the four basic raw materials of the chemical industry (the other three being coal, limestone, and salt). 85% of all sulfur used is first burned to produce sulfur dioxide for further processing for sulfuric acid production; 80% of the sulfuric acid is used in fertilizer production. Sulfur dioxide is also used in leaching ores, bleaching cloth and food products, and it is an important intermediate chemical for the chemical industry. In the U.S. demand for sulfur is increasing primarily to meet increased use of sulfur as sulfuric acid in processing phosphatic fertilizers. The sulfur produced by mining methods accounted to 54% of the domestic production, recovered elemental sulfur accounted for 34%, and by-product sulfuric acid accounted for 9% the remainder of production is in the form of pyrites, sulfur dioxides and hydrogen sulfide.
In the past high speed vacuum type centrifuges have been used for gas and isotope separation. In a gas centrifuge, a steep radial pressure gradient is established, consequently a mixture of two gas streams with different molecular weights were separated. The gas separation by mass diffusion utilizing centrifuge methods required very high electric power consumption.
The present invention provides a method for recovery of the flue gas waste heat energy for producing electric power and utilizing this power for cleaning the flue gas by separation and liquefaction of the sulfur dioxide and as desired part of the carbon dioxide gas.
The present invention utilizes high voltage and high frequency electrode screens to neutralize the electrostatic charge of the particulate matter and the gas molecules after they leave the electrostatic precipitator. A gas cooler provides means for recovery of the waste heat energy to drive a gas power expander, providing the refrigeration effect to cool the flue gases, as well as the electric power required for the sulfur dioxide gas separation and liquefaction system. Centrifuge gas separators, are used to separate heavier mixture of the flue gases, basically enriched carbon dioxide fraction with sulfur dioxide, and use of compression and cooling means to liquefy the sulfur dioxide and as desired part of the carbon dioxide. The lighter mixture of the the gases, basically, enriched nitrogen fraction, then induced in the cooling tower strong draft for an embedded release in the atmosphere. The present invention provides an economical solution to meet the Clean Air Act standards, to reduce the flue gas emissions, and to continue using the high sulfur coal as a reliable source of energy, also to recover up to 99 percent of sulfur dioxide and as desired percent of the carbon dioxide. Liquefied sulfur dioxide maybe used for further processing for sulfuric acid and sulfur element production, and liquefied carbon dioxide maybe used for further processing for use in beverage industries, sugar refinery, fertilizers, fire extinguishers, dry ice, and many other uses. The present invention provides the means to recover valuable by-products from the flue gas cleaning system, and it is understood that the scope of the invention applies to numerous applications where boiler flue gases are exhausted.